1. Field of the Invention
The present inventions relates generally to a disk drive and write speed control method, and more particularly, to an optical disk drive and write speed control method for writing information to a disk at a constant angular velocity.
2. Description of the Related Art
Generally, drive devices for CD-R (Compact Disk-Recordable) and CD-RW (Compact Disk-ReWritable) have used CLV (Constant Linear Velocity) control to write information to the disk, in which the magnetic head moves along a track at a constant linear velocity.
FIG. 1 shows an example of a conventional CD-R disk format. As shown in the drawing, the CD-R disk 1 has a center hole 2 that engages a spindle motor of the CD-R drive. The CD-R disk 1 is rotated by the rotation of the spindle motor. Tracks 3 are formed in the shape of a spiral on the CD-R disk 1. Information is recorded along these tracks 3.
FIG. 2 is an enlarged oblique view of a track portion of a disk. As shown in the drawing, a pre groove 4 is formed along each track 3 on the disk 1 and is defined by curved side walls undulating at a regular interval. The regularly undulating side walls of the pre-groove produce a wobble signal.
ATIP (Absolute Time in Pre-groove) data is modulated on the wobble signal on the wobble signal. The ATIP data is bi-phase modulated as well as frequency modulated before being recorded.
FIGS. 3A, 3B and 3C show ATIP data, wobble signal and a digitized wobble signal, that is, a wobble pulse, respectively.
FM demodulation of the wobble signal shown in FIG. 3B yields the signal shown in FIG. 3A. The signal shown in FIG. 3A is bi-phase modulated ATIP data. The wobble signal shown in FIG. 3B is digitized to yield a wobble pulse like that shown in FIG. 3C.
FIGS. 4A, 4B and 4C illustrate a CLV writing operation. The horizontal axis represents a radial direction of the disk 1, that is, a distance in a direction represented by double-headed arrow A in the drawing. FIG. 4A shows an FG (Frequency Generator) pulse, FIG. 4B shows a wobble pulse and FIG. 4C shows a write clock. The FG pulse is a periodic pulse keyed to the rotation of the spindle motor that rotates the disk 1.
In CLV writing, the rotation of the disk 1 is controlled in such a way that the linear velocity of the tracks 3 is constant for all tracks including the innermost and outermost tracks. As a result, the FG pulse shown in FIG. 4A has a variable cycle.
In addition, because the linear velocity of the tracks 3 is constant for the innermost and outermost tracks, as shown in FIG. 4B the wobble pulse becomes constant.
Further, because the linear velocity of the tracks 3 is constant for the innermost and outermost tracks, as shown in FIG. 4C, the write recording density becomes constant as well.
The conventional CD-R, CD-RW disk device, because it writes data using the CLV system, is required to change the rotation of the disk 1 depending on the position of the light beam or optical head. Moving the light beam from a position on an outer track to a position on an inner track during a seek operation, for example, requires changing the rotational speed of the disk 1 so as to maintain a constant linear velocity. In such a situation it takes time for the rotation of the disk 1 to stabilize, with the result that it takes additional time to write information to the disk.
In addition, in order to change the rotation of the disk 1 the rotation of the spindle motor has to be increased or decreased as necessary. This adjustment of the speed of rotation places an additional load on the spindle motor, both shortening the useful life of the motor as well as increasing the consumption of electrical power.
Accordingly, it is a general object of the present invention to provide an improved and useful optical disk drive and write speed control method in which the disadvantages described above are eliminated.
Another and more specific object of the present invention is to provide an improved and useful optical disk drive and write speed control method in which a rotational speed of a motor that rotates an optical disk is controlled so as to be constant and a writing frequency at which information is written to the optical disk is controlled in such a way that the information written to the optical disk with a predetermined optimum recording density.
The above-described objects of the present invention are achieved by an optical disk device comprising:
a motor that rotates an optical disk;
motor control means for making constant a rotational speed of the motor; and
write control means for changing a write frequency of information written to the optical disk such that writing of the information onto the optical disk is made at a substantially constant recording density, irrespective of a track on which the information is recorded.
Additionally, the above-described objects of the present invention are also achieved by the optical disk device as described above, further comprising:
wobble signal detecting means for detecting a wobble signal recorded along a track formed on the optical disk;
sync signal detecting means for detecting a first sync signal recorded at a constant interval on the track formed on the optical disk;
write clock generating means for generating a write clock according to an optical head position on the optical disk, the write clock generating means generating the write clock from the wobble signal detected by the wobble signal detecting means;
second sync signal generating means for generating a second sync signal according to the write clock generated by the write clock generating means:
phase difference detecting means for detecting a phase difference between the first sync signal and the second sync signal; and
write clock control means for controlling the write clock generated by the write clock generating means according to the phase difference detected by the phase difference detecting means.
Additionally, the above-described objects of the present invention are also achieved by the optical disk device as described above, further comprising synchronization detecting means for detecting a synchronization of the first sync signal and the second sync signal, wherein the write control means writes information to the optical disk after synchronization has been detected by the synchronization detecting means.
Additionally, the above-described objects of the present invention are also achieved by an optical disk write control method for controlling the speed at which information is written to tracks formed on an optical disk by an optical disk device, comprising the steps of:
rotating the optical disk at a constant angular velocity; and
changing the information recording frequency between outer tracks and inner tracks of the optical disk so as to achieve a constant linear recording density.
Additionally, the above-described objects of the present invention are also achieved by the optical disk write control method as described above, further comprising the steps of:
detecting a wobble signal recorded along a track formed on the optical disk;
generating a write clock according to an optical head position on the optical disk from the wobble signal detected at the wobble signal detecting step;
generating a second sync signal according to the write clock generated at the write clock generating step;
detecting a first sync signal recorded at a constant interval on the track formed on the optical disk;
detecting a phase difference between a first sync signal and a second sync signal; and controlling the write clock generated at the write clock generating step according to the phase difference detected at the phase difference detecting step.
Additionally, the above-described objects of the present invention are also achieved by the optical disk write control method as described above, further comprising the steps of:
detecting a synchronization of the first sync signal and the second sync signal; and
commencing writing information to the optical disk after synchronization has been detected at the synchronization detecting step.
According to the invention described above, there is no need to change the speed of rotation of the disk in response to the position of the optical head. As a result, the time needed to write information to the optical disk can be shortened.
In addition, the spindle motor does not accelerate rapidly, so power consumption can be reduced and the useful life of the motor prolonged.
Further, the write frequency decreases toward the inner side of the disk and increases toward the outer side of the disk. Accordingly, by setting the write frequency at the inner side to a normal write frequency the write frequency at the outer side can be increased, thereby increasing the overall speed of data transfer.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.